# EppsNet Archive: Programming

## Competitive Programming: POJ 1905 – Expanding Rods

Description When a thin rod of length L is heated n degrees, it expands to a new length L’=(1+n*C)*L, where C is the coefficient of heat expansion. When a thin rod is mounted on two solid walls and then heated, it expands and takes the shape of a circular segment, the original rod being the chord of the segment. Your task is to compute the distance by which the center of the rod is displaced. Input The input contains multiple lines. Each line of input contains three non-negative numbers: the initial lenth of the rod in millimeters, the temperature change in degrees and the coefficient of heat expansion of the material. Input data guarantee that no rod expands by more than one half of its original length. The last line of input contains three negative numbers and it should not be processed. Output For each line of input, output one… Read more →

## Competitive Programming: CodeSignal – footballGroupStatictics (A World Cup SQL Challenge)

Description You are creating a website that will help you and your friends keep track of the results of soccer games from all around the world. You store all results of one group in a table, results. You want to sort the teams in a complex way – first by points, then by total goal differences, and then by total goals. If all of these parameters are equal, sort the teams alphabetically. The results table contains the following columns: first_team – the name of the first team; second_team – the name of the second team; first_team_score – the number of goals scored by the first team; second_team_score – the number of goals scored by the second team. Here the primary key is the pair (first_team, second_team). Return the list of team names sorted in the way described above. Note: see three points for a win to understand how points are… Read more →

## 11,000 New Computer Science Teachers Considered Harmful?

Here’s the start of an email I got from Code.org: We’re kicking off our summer workshops to prepare 11,000 new CS teachers. Last month we welcomed over 600 teachers, facilitators, and Regional Partners to Atlanta, GA for our largest TeacherCon ever. On top of TeacherCon, we also have 350 K-5 workshops and 167 workshops for middle and high school teachers planned this summer, where we expect an additional 10,000 teachers who plan to begin teaching computer science for the first time this fall! This is heralded with an exclamation point, like it’s exciting news, but as a computer science person, I can’t get excited about it. Why do we want kids to be taught computer science by 11,000 teachers who know little or nothing about computer science? How can someone teach something that they themselves don’t do? See if you can get excited about any of the following possibilities: 11,000… Read more →

## Competitive Programming: CodeSignal – canScore (A World Cup Challenge)

Description Your friend is a soccer fan and you were watching some World Cup matches with him. You liked this game, but the rules are very complicated for you, so you decided just to try to guess whether the given attack will end with a goal or not. In the beginning, the ball is in the attacking team’s goalkeeper’s hands. On the attacking team, there’s a very talented goalscorer, who is waiting for his chance at the other end of the field. His teammates want to give him the ball so he can score. They can move the ball by passing it one to another along a straight line, but the defender can steal the pass if he is closer than d to the ball at any point throughout the pass. Now you want to know if the attacking team can score or not. Formally, you are given the coordinates… Read more →

## Competitive Programming: POJ 3281- Dining

Description Cows are such finicky eaters. Each cow has a preference for certain foods and drinks, and she will consume no others. Farmer John has cooked fabulous meals for his cows, but he forgot to check his menu against their preferences. Although he might not be able to stuff everybody, he wants to give a complete meal of both food and drink to as many cows as possible. Farmer John has cooked F (1 <= F <= 100) types of foods and prepared D (1 <= D <= 100) types of drinks. Each of his N (1 <= N <= 100) cows has decided whether she is willing to eat a particular food or drink a particular drink. Farmer John must assign a food type and a drink type to each cow to maximize the number of cows who get both. Each dish or drink can only be consumed by… Read more →

## Competitive Programming: POJ 2455 – Secret Milking Machine

Description Farmer John is constructing a new milking machine and wishes to keep it secret as long as possible. He has hidden in it deep within his farm and needs to be able to get to the machine without being detected. He must make a total of T (1 <= T <= 200) trips to the machine during its construction. He has a secret tunnel that he uses only for the return trips. The farm comprises N (2 <= N <= 200) landmarks (numbered 1..N) connected by P (1 <= P <= 40,000) bidirectional trails (numbered 1..P) and with a positive length that does not exceed 1,000,000. Multiple trails might join a pair of landmarks. To minimize his chances of detection, FJ knows he cannot use any trail on the farm more than once and that he should try to use the shortest trails. Help FJ get from the barn… Read more →

## Competitive Programming: POJ 2195 – Going Home

Description On a grid map there are n little men and n houses. In each unit time, every little man can move one unit step, either horizontally, or vertically, to an adjacent point. For each little man, you need to pay a \$1 travel fee for every step he moves, until he enters a house. The task is complicated with the restriction that each house can accommodate only one little man. Your task is to compute the minimum amount of money you need to pay in order to send these n little men into those n different houses. The input is a map of the scenario, a ‘.’ means an empty space, an ‘H’ represents a house on that point, and am ‘m’ indicates there is a little man on that point. You can think of each point on the grid map as a quite large square, so it can… Read more →

## Competitive Programming: POJ 3169 – Layout

Description Like everyone else, cows like to stand close to their friends when queuing for feed. FJ has N (2 <= N <= 1,000) cows numbered 1..N standing along a straight line waiting for feed. The cows are standing in the same order as they are numbered, and since they can be rather pushy, it is possible that two or more cows can line up at exactly the same location (that is, if we think of each cow as being located at some coordinate on a number line, then it is possible for two or more cows to share the same coordinate). Some cows like each other and want to be within a certain distance of each other in line. Some really dislike each other and want to be separated by at least a certain distance. A list of ML (1 <= ML <= 10,000) constraints describes which cows like… Read more →

## Competitive Programming: POJ 1125 – Stockbroker Grapevine

Description Stockbrokers are known to overreact to rumors. You have been contracted to develop a method of spreading disinformation amongst the stockbrokers to give your employer the tactical edge in the stock market. For maximum effect, you have to spread the rumors in the fastest possible way. Unfortunately for you, stockbrokers only trust information coming from their “Trusted sources” This means you have to take into account the structure of their contacts when starting a rumor. It takes a certain amount of time for a specific stockbroker to pass the rumor on to each of his colleagues. Your task will be to write a program that tells you which stockbroker to choose as your starting point for the rumor, as well as the time it will take for the rumor to spread throughout the stockbroker community. This duration is measured as the time needed for the last person to receive… Read more →

## Competitive Programming: POJ 2488 – A Knight’s Journey

Description Background The knight is getting bored of seeing the same black and white squares again and again and has decided to make a journey around the world. Whenever a knight moves, it is two squares in one direction and one square perpendicular to this. The world of a knight is the chessboard he is living on. Our knight lives on a chessboard that has a smaller area than a regular 8 * 8 board, but it is still rectangular. Can you help this adventurous knight to make travel plans? Problem Find a path such that the knight visits every square once. The knight can start and end on any square of the board. Input The input begins with a positive integer n in the first line. The following lines contain n test cases. Each test case consists of a single line with two positive integers p and q, such… Read more →

## Competitive Programming: POJ 1159 – Palindrome

Description A palindrome is a symmetrical string, that is, a string read identically from left to right as well as from right to left. You are to write a program which, given a string, determines the minimal number of characters to be inserted into the string in order to obtain a palindrome. As an example, by inserting 2 characters, the string “Ab3bd” can be transformed into a palindrome (“dAb3bAd” or “Adb3bdA”). However, inserting fewer than 2 characters does not produce a palindrome. Input Your program is to read from standard input. The first line contains one integer: the length of the input string N, 3 <= N <= 5000. The second line contains one string with length N. The string is formed from uppercase letters from ‘A’ to ‘Z’, lowercase letters from ‘a’ to ‘z’ and digits from ‘0’ to ‘9’. Uppercase and lowercase letters are to be considered distinct.… Read more →

## Competitive Programming: POJ 2663 – Tri Tiling

Description In how many ways can you tile a 3xn rectangle with 2×1 dominoes? Here is a sample tiling of a 3×12 rectangle. Input Input consists of several test cases followed by a line containing -1. Each test case is a line containing an integer 0 <= n <= 30. Output For each test case, output one integer number giving the number of possible tilings. Sample Input 2 8 12 -1 Sample Output 3 153 2131 Link to problem Solution below . . . Read more →

## Developers Should Abandon Agile

No matter what framework or method your management thinks they are applying, learn to work this way: Produce running, tested, working, integrated software every two weeks, every week. Build your skills until you can create a new fully operational version every day, twice a day, multiple times a day. Keep the design of that software clean. As it grows, the design will tend to become complex and crufty. Resist and reverse this tendency consciously, refactoring in tiny continuous steps, all the time, so that your rate of progress is as steady and consistent as possible. Use the current increment of software as the foundation for all your conversations with your product leadership and management. Speak in terms of what’s ready to go, and in terms of what they’d like you to do next. This is the development team’s best hope for a reasonable life. By keeping the software always ready… Read more →

## Competitive Programming: POJ 1426 – Find The Multiple

Description Given a positive integer n, write a program to find out a nonzero multiple m of n whose decimal representation contains only the digits 0 and 1. You may assume that n is not greater than 200 and there is a corresponding m containing no more than 100 decimal digits. Input The input file may contain multiple test cases. Each line contains a value of n (1 <= n <= 200). A line containing a zero terminates the input. Output For each value of n in the input print a line containing the corresponding value of m. The decimal representation of m must not contain more than 100 digits. If there are multiple solutions for a given value of n, any one of them is acceptable. Sample Input 2 6 19 0 Sample Output 10 100100100100100100 111111111111111111 Link to problem Solution below . . . Read more →

## Competitive Programming: POJ 2084 – Game of Connections

Description This is a small but ancient game. You are supposed to write down the numbers 1, 2, 3, . . . , 2n – 1, 2n consecutively in clockwise order on the ground to form a circle, and then, to draw some straight line segments to connect them into number pairs. Every number must be connected to exactly one another. And, no two segments are allowed to intersect. It’s still a simple game, isn’t it? But after you’ve written down the 2n numbers, can you tell me in how many different ways can you connect the numbers into pairs? Life is harder, right? Input Each line of the input file will be a single positive number n, except the last line, which is a number -1. You may assume that 1 Read more →

## Competitive Programming: USACO Big Barn

Farmer John wants to place a big square barn on his square farm. He hates to cut down trees on his farm and wants to find a location for his barn that enables him to build it only on land that is already clear of trees. For our purposes, his land is divided into N x N parcels. The input contains a list of parcels that contain trees. Your job is to determine and report the largest possible square barn that can be placed on his land without having to clear away trees. The barn sides must be parallel to the horizontal or vertical axis. EXAMPLE Consider the following grid of Farmer John’s land where ‘.’ represents a parcel with no trees and ‘#’ represents a parcel with trees: 1 2 3 4 5 6 7 8 1 . . . . . . . . 2 . # .… Read more →

## Competitive Programming: POJ 1654 – Area

Description Consider an infinite full binary search tree (see the figure below), the numbers in the nodes are 1, 2, 3, …. In a subtree whose root node is X, we can get the minimum number in this subtree by repeating going down the left node until the last level, and we can also find the maximum number by going down the right node. Now you are given some queries as “What are the minimum and maximum numbers in the subtree whose root node is X?” Please try to find answers for the queries. Input In the input, the first line contains an integer N, which represents the number of queries. In the next N lines, each contains a number representing a subtree with root number X (1 Read more →

## Competitive Programming: POJ 2242 – The Circumference of the Circle

Description To calculate the circumference of a circle seems to be an easy task – provided you know its diameter. But what if you don’t? You are given the cartesian coordinates of three non-collinear points in the plane. Your job is to calculate the circumference of the unique circle that intersects all three points. Input The input will contain one or more test cases. Each test case consists of one line containing six real numbers x1,y1,x2,y2,x3,y3, representing the coordinates of the three points. The diameter of the circle determined by the three points will never exceed a million. Input is terminated by end of file. Output For each test case, print one line containing one real number telling the circumference of the circle determined by the three points. The circumference is to be printed accurately rounded to two decimals. The value of pi is approximately 3.141592653589793. Sample Input 0.0 -0.5… Read more →

## Teaching Computer Science: How to Get Top-Notch Teachers in the Classroom

I read something every day where educators and/or elected officials are talking about the importance for our kids, our country, our future, etc., of teaching computer science, the sticking point being an extreme shortage of qualified teachers. A person entering the workforce with a computer science degree is unlikely to go into teaching because of the opportunity cost: they can earn a lot more money as a software engineer. The likelihood of getting a mid-career tech industry professional to switch into teaching is even lower. Teacher salaries are based in large part on years of service. A mid-career person switching into teaching is not going to get a mid-career teacher’s salary, they are going to get a first-year teacher’s salary. So here’s the idea: Give CS professionals the opportunity to apply their years in industry to years of service as a teacher. It’s still a pay cut going from software… Read more →

## Teaching Computer Science: The Phones Aren’t Helping You

I’m volunteering a couple mornings a week at a local high school, helping out with computer science classes. The way the classes are taught, via an online curriculum, provides a great temptation to kids to get off-task, which they do, usually by entertaining themselves with their phones. They get off-task in other ways too — web surfing, doing homework for other classes — but the main distractor is the phones . . .   “As I mentioned before, I worked with another CS class a couple years ago. No phones allowed in the classroom. “I remember one day the assistant principal was in class observing . . . a student had a phone out, looking at it . . . he was holding it under the table so no one could see it, but this guy, the assistant principal, he did see it. “Oh man, did he hit the roof!… Read more →

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